At present, SDH/SONET has been widely used in a backbone layer of a transport network. As advantages such as a perfect network equipment management function, a powerful networking ability, and a strong network self-healing ability possessed by an SDH/SONET system are all implemented via overheads in the frame thereof, transmission and processing of the overheads are of great significance for the transmission of SDH/SONET signals.
FIG. 1 is a schematic diagram illustrating a signal processing device of an SDH/SONET system. As shown in FIG. 1, the SDH/SONET signal processing device includes the following modules:
a signal processing unit 200, for receiving or transmitting SDH/SONET optical signals, and implementing the separation and synthesis of payload data and overheads of an SDH/SONET signal;
a payload data processing unit 300, for receiving and processing the SDH/SONET payload data separated by the signal processing unit 200, or generating payload data to be transmitted, and transmitting the payload data to be transmitted to the signal processing unit 200; and
an overhead processing unit 400, for receiving and processing the SDH/SONET overheads separated by the signal processing unit 200, or generating the overheads to be transmitted, and transmitting the overheads to the signal processing unit 200.
It should be noted that, typically, the signal processing unit 200, the payload data processing unit 300, and the overhead processing unit 400 of an SDH/SONET signal processing device are deployed in different hardware daughter boards of a system device, and such hardware daughter boards are interconnected via a motherboard. Therefore, a payload data bus between unit 200 and unit 300 as well as an overhead bus between unit 200 and unit 400 are both implemented through buses on the system motherboard.
Internal structures of the signal processing unit 200 and the overhead processing unit 400 are further described hereinafter. Wherein, the signal processing unit 200 further includes:
an optical receiving module 201, for performing an O/E (optical/electrical) conversion of an SDH/SONET signal;
an optical transmitting module 202, for performing an E/O (electrical/optical) conversion of an SDH/SONET signal;
a serial/parallel conversion module 203, for performing a S/P (serial/parallel) conversion of an SDH/SONET electrical signal;
a parallel/serial conversion module 204, for performing a P/S (parallel/serial) conversion of an SDH/SONET electrical signal;
a signal processing module 205, for performing a separation or a synthesis of the overheads and the payload data;
a receiving overhead storage 207 and a transmitting overhead storage 208 for storing the overheads;
an overhead output module 209, for transmitting the overheads to the overhead processing unit 400; and
an overhead input module 210, for receiving the overheads from the overhead processing unit 400.
Wherein, the overhead processing unit 400 further includes:
a receiving overhead processing module 401, for processing received overheads; and
a transmitting overhead processing module 402 for generating overheads to be transmitted.
The full working flow of the above SDH/SONET signal processing device is described hereinafter in detail.
The signal processing procedure of the signal processing device in the receiving direction is as follows: after receiving an SDH/SONET optical signal, the optical receiving module 201 implements an O/E conversion first, and then transmits the electrical signal to the serial/parallel conversion module 203; After implementing an S/P conversion, the serial/parallel conversion module 203 transmits the outputted parallel SDH/SONET electrical signals to the signal processing module 205; the signal processing module 205 separates the overheads from the payload data of the parallel SDH/SONET electrical signals, submits the payload data to the payload data processing unit 300 for processing via the payload data bus, and outputs the separated Section OverHead (SOH) or Path OverHead (POH) to the receiving overhead storage 207; after extracting the stored overheads from the receiving overhead storage 207, the overhead output module 209 generates a frame header signal and a timing signal corresponding to the overheads, then the overhead output module 209 outputs the frame header signal and the timing signal via a parallel overhead bus on the system motherboard, to the receiving overhead processing module 401 of the overhead processing unit 400 for processing.
The signal processing procedure of the signal processing device in the transmitting direction by the signal processing device is as follows: when a signal is to be transmitted, the transmitting overhead processing module 402 of the overhead processing unit 400 outputs generated overheads as well as a frame header and a timing signal corresponding to the overheads to the overhead input module 210 of the signal processing unit 200 via the parallel overhead bus on the system motherboard; the overhead input module 210 transmits the received parallel overheads to the transmitting overhead storage 208; after extracting the parallel overheads from the transmitting overhead storage 208, the signal processing module 205 synthesizes the extracted overheads with payload data from the payload processing unit 300, generates a set of parallel SDH/SONET electrical signals, and then transmits the parallel signals to the parallel/serial conversion module 204; the parallel/serial conversion module 204 converts the parallel SDH/SONET electrical signals into a serial signal, and then transmits the serial signal to the electrical/optical conversion module 202; finally, the electrical/optical conversion module 202 conducts an E/O conversion for the received serial signal before sending the converted signal to an optical fibre.
As overheads of an SDH/SONET frame perform OAM (Operation, Administration and Maintenance) functions of the SDH/SONET system, it is of great significance to transmit the overheads from the signal processing unit 200 to the overhead processing unit 400 timely, safely and reliably. At present, no specific protocol has been put forward on the specification of this overhead bus while each manufacturer gives the definition of the overhead bus based on its own specifications. Moreover, as the volume of overheads of an SDH/SONET frame is large, a high-speed parallel bus on the system motherboard needs to be employed such that all the overheads in the frame structure of SDH/SONET could be transmitted to the overhead processing unit for processing. Meanwhile, in order to implement the receiving alignment of overheads on the high-speed parallel bus, it needs to insert channel associated system timing and frame-header signals in the parallel overhead bus. This, however, will result in numerous buses on the system motherboard, which increases the complexity and difficulty of system design. Moreover, it impossible to conduct bit error detection using the above signal processing device, which is unfavourable for locating system failures, thus the transmission safety of system overheads can not be guaranteed.